Comparative study of heavy metals concentration in topsoil of urban green space and agricultural land uses

The main objective of this study was to determine the concentration of cadmium, chromium, copper, nickel, lead, and zinc in surface soils of two land uses including agricultural and urban green space in Semnan Province, Iran. For this purpose, the soil samples of 27 urban green space and 47 agricultural fields were collected and analyzed. The correlation coefficients, analysis of variance, principal component analysis, cluster analysis, and geoaccumulation index were utilized to compare the mean values in the two land uses and pinpoint the possible sources of contamination in the study area. The average contents of Cd, Cu, Cr, Ni, Pb, and Zn in green space soils were 0.1, 24.9, 78.7, 28.2, 22.1, and 82.1 mg/kg, respectively, while the mean concentrations of Cd, Cu, Cr, Ni, Pb, and Zn in agricultural soils were 0.3, 24.3, 83.7, 33.3, 18.1, and 80.4 mg/kg, respectively. The mean concentrations of lead, copper, and zinc were higher in urban green space in comparison with those of agricultural fields, while it was vice versa for chromium, cadmium, and nickel. In general, significant, but weak, correlations were observed between Zn with Pb (r = 0.53) and Cu (r = 0.61) and Ni with Cr (r = 0.55) and Cu(r = 0.51). The main sources of contamination turned out to be both natural and anthropogenic as the results of correlation coefficients, principal component analysis, and cluster analysis showed. That is to say, chromium and nickel had emanated from natural while the sources of cadmium, lead, and zinc could be attributed to anthropogenic activities. For the case of copper, both natural and anthropogenic activities were influential; however, the role of human activities was more effective. The results of contamination assessment showed that heavy metal contamination in agricultural land use was higher than green space indicating the role of human activities in this respect.